EFFECT OF D-ALPHA-TOCOPHEROL ANALOGS ON LIPOXYGENASE-DEPENDENT PEROXIDATION OF PHOSPHOLIPID-BILE SALT MICELLES

In order to know whether or not vitamin E acts as an effective antioxi dant in lipoxygenase-dependent peroxidation of phospholipids, the effe ct of vitamin E and vitamin E analogues, 2,2,5,7,8-pentamethyl 6-hydro xychroman (PMC) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox C), was investigated in enzymatic lipid peroxidation of b ile saft micelles of pig liver phosphatidylcholine (PC) using soybean lipoxygenase. 1 5-Hydroperoxy-5,8,11,13-eicosatetraenoic acid was excl usively produced by the reaction with the PC molecular species contain ing arachidonic acid moiety, indicating that the hydroperoxidation of pig liver PC entirely progresses through the enzymatic reaction. PMC s uppressed the accumulation of PC-hydroperoxides (PC-OOH) more efficien tly than either d-alpha-tocopherol (alpha-Toe) or Trolox C, and 50% in hibition concentration by PMC was close to that of quercetin, a known lipoxygenase inhibitor from natural origin. The antioxidant activity o f PMC was also superior to that of either alpha-Toe or Trolox C in fer rous ion-induced nonenzymatic oxidation of PC micelles in the presence of a trace amount of PC-OOH, although the radical-scavenging activiti es of these compounds in solution were similar or comparable to one an other. In conclusion, PMC is more effective than alpha-Toe as an inhib itor of lipoxygenase reaction with phospholipids and of autoxidation i n phospholipids. The phytyl chain of alpha-Toc seems to be unfavorable for exerting an inhibitory effect on lipoxygenase reaction with phosp holipid-bile salt micelles.